My invention relates to an electrical assembly including a conductor pattern bonded to a non-metallic substrate in some areas but not bonded to the non-metallic substrate in other areas, and to a method of fabricating such assembly, and, more particularly, to such assembly and method wherein a conductor pattern is formed from a metallic sheet which is bonded to a non-metallic substrate by means of a eutectic bonding technique.
Various eutectic bonding techniques exist for bonding a metallic sheet to a non-metallic substrate. These techniques all share in common the formation of a molten eutectic alloy, typically derived in part from the metallic sheet, between the sheet and the substrate at an elevated temperature. Such elevated temperature is near, but somewhat below, the melting point of the metallic sheet. The molten eutectic alloy wets the non-metallic substrate and thus assures a strong bond between sheet and substrate.
It is known that a metallic sheet, when heated to an elevated temperature as it is being bonded to a substrate with a eutectic bonding technique, is likely to plastically conform to the shape of the substrate. This is desirable to attain a uniform bond between the metallic sheet and the substrate. However, there are instances in which it would be advantageous to ensure that selected areas of a metallic sheet did not plastically conform to the shape of the substrate and consequently become bonded to the sheet. For example, where the metallic sheet is patterned to implement a conductor pattern upon which heat-producing electrical devices, such as power transistors, are usually mounted and which includes an electrical interconnect member, it would be desirable to have the interconnect member bridge over part of the upper surface of the non-metallic substrate. This would enable the conductor pattern to withstand higher voltage, due to an increased distance of separation along the surface of the substrate between the interconnect member and a metallic heat sink at electrical ground, on which the substrate is typically disposed.